1. Field of the Invention
This invention relates to a process for thermal treatment of solid particles in a fluidized bed characterized by thermal treatment in multiple temperature zones forming a lighter weight fraction of solids or a gas or vapor and a heavier weight fraction of solids, relative to the average weight of contents in the bed. The solids are fed to a fluidized bed supported on a bed support having at least one region of opposing downwardly sloping portions which converge in their lower portions into the opening of a heavier particle discharge conduit. A discrete fluid fuel fed flame is maintained in the localized region above the heavier particle discharge conduit opening. The process of this invention provides for treatment of solid particles at multiple temperatures within a single fluidized bed and aids in the separation and withdrawal of solids of differing size-density relationships resulting from such thermal treatment. The process is particularly useful in incineration, calcining, solid particle reclamation, and metallic ore separation.
2. Description of the Prior Art
Fluidized beds are used in a large number of chemical processes and in the gasification or liquefaction of various solids such as coal and shale. Sloping bed supports have previously been used in the ash agglomerating fluidized bed apparatus and processes, such as taught by U.S. Pat. Nos. 4,229,289; 3,935,825; and 2,906,608.
Combustion of liquid fuel in a fluidized bed resting upon a sloping bed support wherein the fuel is injected from a central opening at the bottom of a conical support or in the sloping side regions is taught by U.S. Pat. No. 3,417,978. The '978 patent teaches that such a fluidized bed aids complete combustion of liquid fuel by atomization of the fuel for dispersal throughout the bed for burning. U.S. Pat. No. 4,284,401 teaches combustion of natural or manufactured gas in a fluidized bed and teaches control of fuel carrying air with air-fuel diffusion throughout the bed for combustion. These two patents emphasize the distribution of fuel throughout the fluidized bed for combustion.
Burner nozzles having central fuel supply tubes and annular oxidant supplies are exemplified by U.S. Pat. Nos. 3,972,690, 3,847,564; and 3,649,206.
Use of a carrier gas to sheath a stream of coating gas in a pyrolytic particle coating apparatus utilizing electric heat is taught by U.S. Pat. No. 4,153,004. U.S. Pat. No. 4,259,925 teaches a fluidized bed reactor having its total gas feed through a central tube with a plurality of ducts to effect laminar flow.